Passive ankle prostheses generally do not enable large adjustments to ankle flexion angles. Although there are prosthetic ankles that enable variation of plantar flexion to accommodate heeled shoes, they are not designed for use with large angles of dorsiflexion for hill ascent. Studies have been conducted to investigate the path of the center of pressure relative to the shank, called the roll-over shape, of able-bodied individuals ascending and descending 0°, 5°, and 10° ramps. It was determined that the best fitting rotation of level ground roll-over shape corresponded with the angle of incline of the ramp for positive inclines of the ankle-foot roll-over shape and for positive and negative inclines of the knee-ankle-foot roll-over shape. Therefore, it is important to be able to accommodate the sagittal angle of the ankle to approximate the ground slope.
Prosthesis wearers routinely encounter sloped terrain in daily life. For instance, driveways are commonly sloped, as are wheelchair-accessible ramps used to access buildings and homes. In the U.S., the Americans with Disabilities Act of 1990 (ADA) provides regulations with respect to slopes to determine what is compliant. For instance, building access ramps should be approximately 5° to be considered in compliance for new construction. Specialized activities, such as construction work, military service, and emergency response, may require ambulation on steeply sloped terrain in a loaded condition. Traditional prosthetic ankles may be inadequate to sustain such terrain, as they are typically designed and tested for walking on level ground, stairs, or slight inclines. Mountaineering, which may be occupational or recreational, may require ambulation on extreme slopes under heavily loaded conditions.
In view of the above discussion, it can be appreciated that it would be desirable to have a prosthetic ankle that enables the user to adjust the flexion angle of the ankle to accommodate inclines and declines.